Physical vapor deposition (PVD) is commonly used within the semiconductor industry, as well as within solar, glass coating, and other industries, in order to deposit a layer over a substrate. Sputtering is a common physical vapor deposition method, where atoms or molecules are ejected from a target material by high-energy particle bombardment and then deposited onto the substrate.
The targets employed for PVD processes erode over time. To ensure uniform layer thickness and characteristics, the magnetic field strength on the target should be constant over the entire target life. However, as substrates are sequentially processed using the same target, the surface of the target is eroded, thereby causing the target to become physically smaller. Thus, the magnetic strength on the target changes over the target life, resulting in varied layer properties among the sequentially processed substrates as the deposition rate tends to increase as the target becomes physically smaller and the magnetic strength changes.
What is needed is the ability to maintain a constant deposition rate over the lifetime of the target.